Adjustment and damping device

ABSTRACT

The invention relates to a controllable adjustment and damping device comprising at least one pressure chamber ( 4 ) filled with hydraulic fluid, a fluid container ( 11 ), a pump ( 5 ) connecting the pressure chamber to the fluid container, a compensating volume ( 8 ) and a return line ( 13 ) with a passthrough valve ( 7 ). An electro-rheological fluid or magneto-rheological fluid is used as a hydraulic fluid ( 6 ) which exerts pressure upon a piston ( 3 ) that juts out into the pressure chamber or on a membrane ( 17 ), the intensity thereof being controlled by the passthrough valve.

The invention relates to a controllable actuating and damping devicecomprising at least a pressure chamber filled with a hydraulic fluid, areserve of fluid, a pump which connects the pressure chamber and thereserve of fluid, a compensating volume and a return passage with apass-through valve in which an electrorheological fluid ormagnetorheological fluid is used as the hydraulic fluid, exerting apressure on a piston projecting into the pressure chamber or on adiaphragm, the intensity of which can be controlled by means of thepassthrough valve.

The invention furthermore relates to an energy converter for convertingmechanical vibration energy into electrical energy.

The invention is directed, in particular, towards an electrorheologicalactuator for improving the control of couplings and gearboxes, primarilyviscous couplings or multi-plate clutches, especially for use inmotor-vehicle construction.

The prior art has disclosed various forms of coupling which operateusing an electrorheological fluid as hydraulic fluid (see, for example,DE 39 22 930 and GB 2 218 758). In electrorheological couplings, theelectrorheological fluid (referred to below as ERF for short) is useddirectly for torque transmission between the surfaces in motion relativeto one another, e.g. the clutch discs. A major disadvantage of such acoupling construction is that very large surfaces are required totransmit high torques since the available electrorheological fluids cantransmit only about 10 kPa of shear stress at the maximum. For a simpledisc clutch, which is intended to transmit a torque of only about 20 Nmfor example, a force-transmitting area of at least 305 cm² wouldtherefore be necessary. However, this large area requires a largeoverall volume of the clutch. Another disadvantage is the pronouncedheating of the electrorheological fluid. This results in a furtherincrease in the energy required to control the clutch. For this reason,couplings based on electrorheological fluids have hitherto only beendeveloped as prototypes for the transmission of low torques.

Said type of clutch is described specifically for use in motor-vehicleconstruction, for decoupling auxiliary units, e.g. for the generator orfan. The very high differential speeds may occur in the region of theclutch discs due to the changes in engine speed, a high torque occurseven in the inactive state of the electrorheological fluid, due to itsbasic viscosity. This limits the possibilities for controlling theclutch.

One object of the invention is to develop an improved actuator forcouplings based on electroviscous fluids as hydraulic fluid which doesnot have the abovementioned disadvantages. In particular, it should bepossible to provide an actuator which allows continuous adjustment, e.g.of multi-plate clutches.

Actuators using hydraulic fluids are known from motor-vehicleconstruction. The so-called ELDRO devices may be mentioned here by wayof example (EMG, AEG). With this type of actuator, a piston with anactuating rod is moved between two end positions by means of thepressure of a hydraulic fluid in a pressure chamber connected to a pump.In this arrangement, the pressure in the pressure chamber is maintainedby a hydraulic pump. An actuator of this kind has the disadvantage thatthe piston can only be moved into two positions and that continuousadjustment of the piston travel is possible only with high outlay onconstruction.

It is a further object of the invention to develop an active damperwhich is capable of active anti-phase compensation of shocks or othermechanical vibrations.

Shock absorbers based on the action of electrorheological fluids aredescribed in many places in the patent literature. One example that maybe referred to is U.S. Pat. No. 5,259,487. In the case of the shockabsorber described there, the electrorheological fluid is forced throughan electrode gap by means of a piston. The pressure drop and hence thedamper force is infinitely variable from a low to a maximum value usingthe electrorheological effect in the electrode gap.

In principle, it is possible by means of electrorheological shockabsorbers to obtain semi-active suspensions whose damping can be variedwithin short time periods. In some cases, the switching time is lessthan 10 msec. Active influencing of the shock-absorber piston is notpossible with the shock absorber mentioned.

The prior art has also disclosed passive engine mounts based onelectrorheological fluids as the hydraulic fluid. See, for example,publication SAE 931324 of the Proceedings of the 1993 Noise andVibration Conference, Travers City, Mich., 10th to 13th May 1993.

The mount mentioned is an adaptive mount which can be switched backwardsand forwards between various states. These so-called ERF mounts do nothave any discernible technical advantage over the conventional hydraulicmounts known from the prior art. On the contrary, the active mountscurrently required for use as engine mounts are those which can, forexample, completely compensate for engine vibrations, such as the secondharmonic of the engine speed in the case of four-cylinder internalcombustion engines.

An engine mount that operates in an optimum manner must furthermorefulfil at least two functions. The natural frequencies of theengine/body caused by load changes or excitation by the roadway must bedamped in an optimum manner in a frequency range typically of about 12Hz. Engine vibrations in the higher-frequency range of about 20 to 100Hz must be isolated in an optimum manner from the chassis and, inparticular, the passenger cell. Particularly in the case of dieselengines, there is a requirement that vibrations in the idling range(diesel clatter) at about 30 Hz should be suppressed.

It is another object of the invention to use the damping property of theactuator in such a way that it is possible with a fundamentallyidentical construction not only to accept and eliminate the mechanicalvibrations, e.g. in the case of use as a passive shock absorber, but,where required, to convert them into electrical energy.

The object is achieved according to the invention by a controllableactuating and damping device which is the subject matter of theinvention and comprises at least a pressure chamber with a piston, or adiaphragm, a reserve of fluid containing a hydraulic fluid, a pump whichconnects the pressure chamber and the reserve of fluid, a compensatingvolume, a return passage with a valve, and an enclosing housing, and ischaracterized in that the hydraulic fluid is an electrorheological fluidor magnetorheological fluid which is pumped by means of the pump, flowsfrom the reserve of fluid into the pressure chamber and, from there,flows via the valve back into the reserve of fluid or else in theopposite direction, in that the pressure of the hydraulic fluid in thepressure chamber acts on the piston or the diaphragm, and in that thevalve is embodied as an ERF or MRF valve by means of which the flow ofthe hydraulic fluid through the return passage is controlled, therebyallowing the pressure of the hydraulic fluid on the piston or diaphragmto be adjusted.

The term electrorheological fluids is intended to indicate dispersionsof finely divided hydrophilic particles in hydrophobic, electricallynon-conductive oils (generally colloidal suspensions of electricallypolarizable, non-conductive particles) which, under the action of anelectric field of sufficiently high electric field strength, rapidly andreversibly change their yield strength or their shear modulus, undercertain circumstances over several orders of magnitude. In the process,the ERF may change from the low-viscosity, via the plastic, to the solidstate of aggregation.

Examples of suitable electrorheological fluids are mentioned in GermanOffenlegungsschriften (German Published Specifications) DE 35 17 281 A1, DE 35 36 934 A 1, DE 39 41 232 A 1, DE 40 26 881 A 1, DE 41 31 142 A1 and DE 41 19 670 A 1.

Both direct-voltage and alternating-voltage fields are used to excitethe electrorheological fluids. The electric power required here iscomparatively low.

To control the flow behaviour of the electrorheological fluid in thecoupling elements, use can be made of a sensor such as that described inGerman Offenlegungsschrift (German Published Specification) DE 36 09 861A 1.

The term magnetorheological fluids (MRF) refers to suspensions of finelydivided magnetic particles with a particle size of a few pm or a few nmin suitable liquids such as mineral or silicone oils, the solids contentof the suspension typically being about 20 to 60% by volume. The flowresistance of magnetorheological fluids changes under the influence of astrong magnetic field as a function of the magnetic field strength.Depending on the type, they reach shear stress values of up to 100 kPa.

According to the invention, the electrorheological or magnetorheologicalfluid is thus not used for torque transmission but as a control medium.Where the controllable actuating device is used for a clutch, thedistance between the discs of the clutch is controlled in a clearlydefined manner by means of the ERF of the actuating device. It istherefore possible, with the device according to the invention, tocontrol both the output speed and the torque of such a clutch withinwide limits, as desired for driving auxiliary units according torequirements, e.g. in motor vehicles.

The use of the device according to the invention as an actuator isdirected, in particular, towards low-frequency movements with afrequency of less than or equal to 1 Hz at amplitudes of preferably 1 to30 mm.

Like a known hydraulic mount, an active engine mount based on theactuating and damping device according to the invention comprises afluid-filled space which is. closed off on one side by a hard-rubberbody. The pump element is intended to allow a continuous volume flowbetween the pressure chamber and the reserve of fluid. The desireddamping, is set by means of the return passage or the ERF or MRF valvesituated in the return passage. Compared with conventional known mounts,which are designed for a particular type of engine or car, there is thepossibility with a mount based on the actuating and damping deviceaccording to the invention to set suitable damping with a single type ofmount, irrespective of the particular type of engine or car. A furtheradvantage of the invention is that the damping can be adjusted activelyto different vibratory excitation or load changes.

The use of the device according to the invention as an active mount isdirected, in particular, at vibrations with a frequency of 200 to 100 Hzand with an amplitude of 0.01 to 0.5 mm.

In particular, it is possible, for the purpose of eliminating relativelyhigh mechanical frequencies by anti-phase activation of theelectrorheological fluid or magnetorheological fluid in relation to theengine vibration to excite a vibration of the hard-rubber mounting whichfully compensates for the vibration of, for example, the engine.

Another object of the invention is the use of the device according tothe invention as an active damper for damping mechanical vibrations.

In this context, the pressure chamber of the device is subjected topressure in such a way that a pressure shock via the piston counteractsa shock on the actuating rod. The acceleration of the actuating rod canbe detected by sensors which are known in principle. The signal obtainedcan be used as an actuating signal for activating the ERF in th eelectrode gap.

The use of the device according to the invention as an active damper isdirected, in particular, at vibrations in a range of 1 to 20 Hz at anamplitude of 1 to 30 mm.

It has furthermore been found that it is a simple matter to vary theconstruction of the actuating and damping device according to theinvention in such a way that it not only converts vibration energy intoheat when damping mechanical vibrations but renders the vibration energyusable by converting it into electrical energy. In the simplest case, agenerator unit is provided in the device instead of the pump connectingthe pressure chamber and the reserve of fluid, this generator unit beingcapable of transmitting mechanical vibrations transmitted to thepressure chamber by the piston, via the drive gear and the shaft of thegenerator unit, to the generator, by means of which the rotary motion ofthe shaft is converted into electrical energy.

Thus, the invention also relates to an energy converter for convertingmechanical vibration energy into electrical energy, comprising at leasta pressure chamber with a piston, or a diaphragm, a reserve of fluidcontaining a hydraulic fluid, a generator unit which connects thepressure chamber and the reserve of fluid with a drive gear, flowpassage, shaft and generator, a compensating volume, a return passage, avalve, and an enclosing housing, characterized in that the hydraulicfluid is an electrorheological fluid or magnetorheological fluid, whichis driven by the compressive or tensile force of the piston or thediaphragm from the pressure chamber, through the flow passage of thegenerator unit, into the reserve of fluid or in the opposite direction,in that the hydraulic fluid flowing through the flow passage drives thedrive gear of the generator unit, and generates current in thegenerator, and in that the valve is embodied as an ERF or MRF valve inwhich the flow of the hydraulic fluid through the return passage iscontrolled.

As an alternative, the energy converter according to the invention cansimply be used as an actuating and damping device if a drive, e.g. anelectric motor, is connected to the shaft of the generator unit insteadof the generator. In this case, the drive gear, the shaft and the motoract as a pump for the hydraulic fluid.

The invention also relates to the use of the energy converter of theinvention for the purpose of generating current from low-frequencymechanical vibrations, in particular with a frequency of about 0.5 to 20Hz, in particular at amplitudes of 1 to 30 mm.

The invention is explained in greater detail below by way of examplewith reference to the figures, in which:

FIG. 1 shows a cross section through an actuating and damping deviceaccording to the invention with a piston as force transmitter.

FIG. 2 shows a cross section through an embodiment of the actuating anddamping device according to the invention with a diaphragm as forcetransmitter.

FIG. 3 shows a cross section through an energy converter according tothe invention for converting mechanical vibration energy into electricalenergy.

FIG. 4 shows a cross section through an embodiment in accordance withFIG. 1 with an MRF valve.

EXAMPLES Example 1

An actuator whose operation is based on an ERF as hydraulic fluid and isused for adjusting a clutch is constructed as follows:

An actuating rod 1, which adjusts the distance between the plates ordiscs of a clutch (not shown), is connected to the piston. A volume flowdependent on rotational speed from the reserve of fluid 11 into thepressure chamber 4 is produced by means of a hydraulic pump 5, which ishere designed as a two-stage vane-cell pump. The pump 5 is driven by theV-belt of an internal combustion engine via a V-belt pulley (not shown).The pressure chamber 4 is closed off by the piston 3, which maintains adefined reaction force by means of a return spring 2.

The electrorheological hydraulic fluid 6 flows back through returnpassages 13, 13′ which contain an electrorheological valve 7 into thereserve of fluid 11 and to the inlet side of the pump 5. The valve 7 isdesigned in such a way that the piston 3 remains in its initial positioneven when the pump 5 is at a high rotational speed and hence at a highvolume flow. The electrorheological valve 7 is formed by theelectrically insulated capacitor plate 12, which is embedded in theinsulator 14, and the inner housing 15, which acts as acounterelectrode. The capacitor plate 12 is connected to the live lineof an external high-voltage supply 9. All the other housing componentsare connected to earth potential.

If a high voltage is applied to the electrorheological valve 7, thestrong electric field in the return passage 13 increases the flowresistance of the ERF, with the result that the pressure in the pressurechamber 4 rises. The piston 3 is extended to an extent dependent on theratio of the pressure force to the spring force of the return spring 2and, in the process, displaces the actuating rod 1, with the result thatthe distance between the discs or plates of the clutch is adjusted in aninfinitely variable manner. The compensating volume 8 is gas-filled andis sealed off from the reserve of fluid 11 by a diaphragm, and it servesto compensate for the volume of the extending or retracting actuatingrod.

Example 2

A variant of the actuating and damping device described in Example 1,for actively damping engine vibrations of vehicles, is shown in thesectional representation in FIG. 2. The construction is identical insignificant parts to that in FIG. 1. A rubber diaphragm 17, which isconnected to the actuating rod 1 via the block 18, is provided here totransmit force between the actuator and, for example, an engine to bedamped (not shown), instead of the combination of piston 3 with returnspring 2. The engine is connected directly to the actuating rod 1. Thehousing 15 is connected to the chassis (not shown in FIG. 2) of thevehicle. If the valve 7 in this device is closed by applying a voltage,the pressure in the pressure chamber 4 will stretch the diaphragm 17,thereby extending the actuating rod 1 and actively counteracting amechanical vibration. The damping can be adapted to the vibrationfrequency by means of ERF valve 7, e.g. by detecting the vibrationsusing suitable sensors and anti-phase activation of the valve 7.

Example 3

The construction shown in Example 1 is modified for use of the device asan energy converter in accordance with FIG. 3 such that a generator isconnected to the impeller 16 and the shaft 19 instead of an engine or aV-belt drive. The device is then operated in such a way that vibrationswhich are transmitted to the pressure chamber 4 by the actuating rod 1and the piston 3, which, where the device is used as a shock absorber,are connected to an engine for example. When the return passages 13, 13′are shut off, the hydraulic fluid is forced through flow passage 20 andthe impeller 16 is driven. The rotary motion of the impeller 16 istransmitted by the shaft 19 to the generator 21, which uses it togenerate current. As illustrated in Example 2, a diaphragm 17 can beprovided for force transmission associated with the mechanicalvibrations instead of the combination of piston 3 and return spring 2.

Example 4

A variant of the actuating and damping device according to theinvention, as shown in Example 1, is shown in the sectionalrepresentation in FIG. 4. Here, the MRF 22 is used instead of the ERF.Accordingly, the ERF valve is replaced by the MRF valve 23. The flowresistance of the MRF is controlled by means of the variable magneticfield strength in the return passages 13 and 13′. As a result, theoperation of the actuating and damping device is fundamentally the sameas that in Example 1.

The MRF valve comprises the coil former 24, the iron parts 25 and 26forming the magnetic high, the MRF return passages 13 and 13′ and themagnetic insulators 27. The electric control current of the coil in thecoil former 24 produces a magnetic field which is passed through theiron parts 25 and 26 forming the yoke. This gives rise to a magneticfield of controllable magnetic-field strength in the return passages 13and 13′, the said magnetic field acting perpendicular to the directionof flow of the MRF. The magnetic insulators 27 are used to prevent amagnetic short circuit in the yoke-forming iron part 26 and to obtain ashomogeneous a magnetic field as possible.

What is claimed is:
 1. Controllable actuating and damping devicecomprising, within a single housing, at least a pressure chamber with apiston, or a diaphragm, a reserve of fluid containing a hydraulic fluid,a pump an optional compensating volume, a return passage with a valve,wherein the hydraulic fluid is an electrorheological fluid ormagnetorheological fluid which the pump is disposed to pump from thereserve of fluid into the pressure chamber and, from there, via thevalve, back into the reserve of fluid or in the opposite direction, andwherein the pressure of the hydraulic fluid in the pressure chamber actson the piston or the diaphragm, and wherein the valve is adapted tocontrol flow resistance of the hydraulic fluid in the return passage. 2.An active damper for damping mechanical vibrations, or a coupling,comprising the device of claim
 1. 3. An active mount for machines andengines comprising the controllable and damping device of claim
 1. 4. Amethod for damping mechanical vibrations which comprises damping saidvibrations with a controllable damping device according to claim
 1. 5. Amethod for actuating a clutch, which comprises actuating said clutchwith a controllable actuator according to claim
 1. 6. Energy converterfor converting mechanical vibration energy into electrical energy,comprising, within a single housing, at least a pressure chamber with apiston, or a diaphragm, a reserve of fluid containing a hydraulic fluid,a generator unit which connects the pressure chamber and the reserve offluid, with a drive gear, flow passage, shaft and generator, acompensating volume, a return passage with a valve, wherein thehydraulic fluid is an ERF or MRF, which in operation is driven by thecompressive or tensile force of the piston or the diaphragm from thepressure chamber, through the generator unit, into the reserve of fluidor in the opposite direction, and wherein the hydraulic fluid flowingthrough the flow passage drives the generator, which generates current,and wherein the valve controls the flow resistance of the hydraulicfluid in the return passage.
 7. A method for generating current fromlow-frequency mechanical vibrations which comprises converting saidvibrations into electrical energy with the energy converter of claim 6.